The disclosed technology relates to lubricants for internal combustion engine, particularly those fueled with biodiesel fuels.
Biodiesel is a general term for fuel-grade materials derived from natural sources such as vegetable oils. They are often fatty acid methyl esters (“FAME”) such as rapeseed methyl ester (“RME”) or soybean methyl ester (“SME”). Biodiesel fuels are becoming more prevalent for fueling of diesel engines. The increased use of diesel passenger vehicles in Europe and elsewhere is in part a cause of this increase. Current European diesel standard allow for 5% bio-diesel component to be incorporated into fuels, with indications that 10% bio-diesel content will be soon permitted.
Simultaneously, there is continued pressure for reducing particulate matter emissions from diesel engines. Euro 5 requirements require reduction in particulate matter to 0.05 g/km. Such levels can only be attained, practically, by use of a diesel particulate filter. These filters require regeneration once they are full of soot, and this is typically achieved by increasing the filter temperature to burn off the soot. The temperature increase is often achieved by post-injection of fuel into the engine cylinder.
However, post-injection of fuel can have the undesirable effect of fuel-dilution of the engine lubricant, as more cylinder wall wetting by the fuel allows more fuel to migrate to and accumulate in the lubricant sump. Bio-diesel components are typically less volatile than conventional mineral diesel fuel, and thus concentration of such components in the sump is exacerbated. In fact, use of bio-diesel fuel (B05, i.e., containing 5% ester) along with post-injection may result in 40% fuel dilution of the lubricant, and the bio-diesel component may account for 50% of the diluent. These high levels of bio-diesel in the oil may lead to increased oxidation and deposit formation associated with the lubricant.
United States application 2006/0223724 (Gatto et al., Oct. 5, 2006) teaches a lubricating oil of reduced phosphorus levels which retains excellent viscosity control; i.e., excellent oxidation stability. The oil comprises a major amount of one or more of a Group II, Group III, Group IV and synthetic ester base stock, 4,4′-methylenebis-(2,6-di-tert-butyl phenol), an alkylated diphenyl amine, a detergent and zinc dialkyldithiophosphate. Optionally an oil soluble organomolybdenum compound can be present, as can additional, different hindered phenolic antioxidants. The lubricant contains about 600 ppm or less phosphorus derived from ZDDP. A number of examples contain all three of ZDDP, a hindered phenol and an aromatic amine
United States application 2009/0111720 (Boffa, Apr. 30, 2009) discloses lubricating oil compositions contaminated with biodiesel fuel wherein the lubricant contains diarylamine compounds to improve oxidative stability. Also disclosed is the optional addition of phenol based antioxidants including 4-methyl-2,6-di-tert-butylphenol and 4,4′-methylenebis-(2,6-di-tert-butylphenol).
United States application 2010/0016193 (Habeeb et al., Jan. 21, 2010) discloses lubricating compositions stabilized against the detrimental effects of biodiesel fuel by using a pre-mixture of two antioxidants, either of which may be phenolic. The phenolic compounds described include mono-phenols as well as bisphenol compounds, including alkylene-bridged materials. Listed types of coupled phenols include 2,2′-bis-(6-t-butyl-4-heptylphenol); 4,4′-bis(2,6-di-t-butyl phenol) and 4,4′-methylene-bis(2,6-di-t-butylphenol). 2,2′-methylene bridged bisphenols are not disclosed. Example 2 describes various combinations of antioxidants evaluated for oxidative resistance in the presence of biodiesel; included among these is an unidentified “bis-phenol.”
United States application 2011/0130316 (Varadaraj et al., Jun. 2, 2011) discloses lubricating compositions stabilized against the detrimental effects of biodiesel fuel by using a combination of organic base, detergent, and antioxidant, selected from hindered amines and hindered phenols. The phenolic compounds described include mono-phenols as well as bisphenol compounds, including alkylene-bridged materials. 2,2′-methylene bridged bisphenols are not disclosed. Example 1 includes bisphenol Ethyl 702, which is identified as 4,4″-methylene-bis(2,6-di-t-butyl phenol).
United States application 2011/0082062 (Habeeb et al. Apr. 7, 2011) discloses a combination of detergent (e.g. alkali metal salicylate) and antioxidant (e.g. aminic antioxidants) to the biodiesel fuel or lubricating oil to improve oxidative resistance. As above, bisphenols are disclosed as part of the broad disclosure of phenolic antioxidants; however alkylene bridged 2,2′-bisphenols are neither disclosed nor exemplified.
United States application 2011/0023351 (Poirier et al., Feb. 3, 2011) discloses antioxidant mixtures of hindered phenol and diphenol for fuels containing biodiesel and biodiesel blends. Diphenols refer to aromatic groups containing two alcohol moieties on a single aromatic ring (e.g. hydroquinones). Bisphenols are not disclosed.
United States application 2010/0269774 (Shinoda et al., Oct. 28, 2010) discloses a lubricating composition containing a combination of phenolic antioxidant and amine-based antioxidant useful in diesel engines fueled with biofuel. Several phenolic antioxidants are disclosed, including 2,6-di-t-butylphenol, 2,2′-methylenebis(4-methyl-6-t-butylphenol), 2,2′-methylenebis(4-ethyl-6-t-butylphenol), 4,4′-bis-(2,6-di-t-butylphenol), and alkyl alcohol esters of 3-(4-hydroxy-3,5-di-t-butyl-phenyl)propionic acid. All experimental examples are carried out with 6-methylheptyl alcohol ester of 3-(4-hydroxy-3,5-di-t-butyl-phenyl)propionic acid.
WO/PCT application 2008/124390A2 (Lubrizol, Oct. 16, 2008) discloses a synergistic combination of a hindered phenolic anti-oxidant and a detergent to improve the oxidation stability of biodiesel fuel.
United States application 2008/0127550 (Li et al., Jun. 5, 2008) discloses stabilized biodiesel fuel composition wherein the stabilizing agent is a combination of: i) one or more compounds selected from the group consisting of sterically-hindered phenolic anti-oxidants; and ii) one or more compounds selected from the group consisting of triazole metal deactivators.
U.S. Pat. No. 6,002,051 (Burjes et al., Dec. 14, 1999) discloses compounds of the general formula
wherein each R1 is a tertiary alkyl group, X, Y, and Z are a hydrocarbon-based group (or hydrogen), R2 is alkylene or alkylidene, and n is 0 to 4. Lubricants and fuels may contain such phenolic compounds.
PCT Publication WO 2003/091365 (Jackson et al., Nov. 6, 2003) discloses a method of operating an internal combustion engine in which an antioxidant composition is introduced into a combustion chamber of the engine. The antioxidant composition contains, among other components, an alkylene or alkylidene coupled sterically hindered phenol oligomer. A normally liquid hydrocarbon fuel is disclosed which may be, among others disclosed, diesel fuel and methyl esters of vegetable or animal oils
The disclosed technology provides a lubricant composition suitable for sump lubricated engines fueled by a liquid fuel which includes a bio-diesel component, which exhibits improved corrosion resistance and improved oxidation resistance in lubricants which contain a portion of the bio-diesel component. This is accomplished by the presence of an alkylene-coupled phenol compound. While a bio-diesel component will typically be prepared from a biological source (an animal or vegetable fat or oil), it is to be understood that the disclosed technology is equally applicable if the bio-diesel component or bio-diesel fuel, such as a fatty acid ester, is prepared from a synthetic source, that is, not derived from an animal or vegetable fat or oil.